In order to be able to walk in wet and/or snowy conditions, footwear exists composed of a single-piece boot made of a thermoplastic material that is sufficiently impermeable to prevent the penetration of water through the boot.
These boots have an intermediate part delimiting a housing for holding the foot, or even the ankle depending on its dimensions, the intermediate part being fitted with an outer sole that improves bond and/or grip on the ground. An inner sole and/or a sock can also be placed inside the boot to improve thermal insulation and comfort.
To limit the risk of ingress of water and/or snow into the footwear, such boots may be fitted with a top sleeve which surmounts in a single piece the intermediate part, the boot then being in the form of a tall boot, the sleeve of which is arranged to extend over at least a part of the user's leg.
To improve the aesthetics of the footwear, the boot can be fitted with an outer upper that extends around the sleeve, particularly in order to conceal it, the outer upper being provided with patterns, textures and/or colors satisfying the user's wishes.
The outer upper may also be adapted to optimize some properties of the footwear, such as impermeability and/or thermal insulation properties, for example by being made from a flexible water repellent and/or insulating textile material.
However, one of the difficulties in making such footwear is to connect the outer upper to the boot without degrading the impermeability and/or thermal insulation provided by the boot to the footwear.
To achieve this, methods are known for making footwear in which the outer upper is attached to the boot at the same time that the boot is formed, for example by vulcanization or molding. Such methods allow to attach the outer upper without changing manufacturing of the boot but they are not fully satisfactory in that they require that the outer upper should be put into position when the boot is formed, which is complex to implement reliably.
To overcome this problem, document WO-2007/007369 discloses that the outer upper can be fixed onto the boot after formation of the boot. Indeed, this document discloses that the lower part of the outer upper can be stitched onto a lip formed on the upper edge of the intermediate part.
However, such an embodiment requires additional operations to maintain the impermeability of the footwear because the holes formed in the lip by the stitches lead to the possibility of water, air and/or moisture penetration inside the boot. To do so, an impermeable coating is glued to the inside of the boot while extending at least over the stitches.
Therefore this appended waterproofing solution increases the complexity of the method of manufacturing the footwear, requiring additional labor and tools associated with high costs. Moreover, the efficiency of such an inner coating is not always guaranteed in the long term, since the coating can deteriorate during use, particularly by friction with the user's foot.